The use of asbestos as diaphragm material in electrolytic chlor-alkali cells is well known. Ordinarily the diaphragms are prepared by vacuum-drawing a slurry of chrysotile asbestos fibers onto a porous cathode, thereby depositing a matte of asbestos on the cathode.
It has been previously taught that polymeric fluorocarbons may be used as binders for asbestos diaphragms. The most relevant technique taught is, in general, to mix a slurry of particulate binder material with the asbestos fibers, then draw or deposit the materials in the form of a matte on the porous cathode, then heat-sinter to effect bonding. Patents which teach the use of binders of polymers for use in asbestos diaphragms are, for example as follows:
U.s. pat. No. 1,942,183 -- teaches use of organic glutinous material as binder for asbestos diaphragms. PA1 U.s. pat. No. 2,731,068 -- teaches impregnation of asbestos fabric with dispersion of polytetrafluoroethylene, followed by heat-sintering. PA1 U.s. pat. No. 2,840,881 -- teaches non-woven asbestos batt having superposed thereon a non-woven batt of polytetrafluoroethylene. PA1 U.s. pat. No. 2,944,956 -- teaches use of the polytetrafluoroethylene (and polymonochlorotrifluoroethylene) screen along with asbestos diaphragm. PA1 U.s. pat. No. 2,945,831 -- teaches mixing of fluorocarbon dispersions (and other polymers) with dispersion of asbestos, then forming a crack-free coalesced film on a substrate. PA1 U.s. pat. No. 3,017,338 -- teaches polymer-bonded asbestos diaphragms and membranes. PA1 U.s. pat. No. 3,097,990 -- teaches, among other things, use of polytetrafluoroethylene dispersions to certain pre-treated asbestos sheets. PA1 U.s. pat. No. 3,153,610 -- teaches preparation of asbestos paper from an aqueous blend of asbestos particles and polymer particles, the polymer being of "ethylenically unsaturated compounds". PA1 U.s. pat. No. 3,551,205 -- teaches addition of polytetrafluoroethylene aqueous emulsion to an asbestos slurry to prepare bonded web for use as a "paper" electrode structure in a voltaic cell.
Other patents which teach the use of fluorocarbon polymers as binders for asbestos in preparing diaphragms or membranes for use in electrolytic cells are, e.g.: U.S. Pat. No. 3,583,891; U.S. Pat. No. 3,694,281; U.S. Pat. No. 3,704,221; and U.S. Pat. No. 3,723,264. These four patents teach mixing of fluorocarbon polymer dispersions with asbestos fibers prior to forming the diaphragm.